The present invention relates to an optical disk for recording/retrieving information through laser light and a manufacturing method thereof, and more particularly to a rewritable compact disk having a ROM area available only for retrieving and a rewritable RAM area, and a manufacturing method thereof.
In the recent years, in addition to audio CD or CD-ROM, CD-R (CD-Recordable) or CD-RW (CD-Rewritable) has been put on the market as recordable media interchangeable with these, and has come into widespread use.
This group is referred to as a CD family, and among media available only for retrieving, there are CDDA, CD-ROM, CD-ROMXA, CDV, CD-I, CD-MIDI and others. The CDDA is a so-called music CD. In the following description, these will sometimes be referred to generically as CD available only for retrieving.
In these CDs available only for retrieving, embossed pit strings including information are previously formed on a substrate made of a translucent polycarbonate or the like by means of a press or the like, and a reflective layer comprising a metallic film made of a precious metal, Al or the like is formed on the pit formed surface, and further a protective layer made of a photo-curing resin is formed thereon. These CDs available only for retrieving have come into widespread use for the purpose of storing and retrieving music, image, data, program and others. The specification on recording on this CD and retrieved signals is prescribed as the CD standard, and a retrieving apparatus according to this standard have become widespread in the form of CD players.
The CD-R or CD-RW, by contrast, is a medium writable by a user. Data on the CD-R is retrievable through a CD-ROM drive mounted in a personal computer or a CD player, but data is writable only once thereon, with the data once recorded being inerasable.
On the other hand, data on the CD-RW is retrievable only by a CD-RW handling drive because of a lower reflectance than that of a CD available only for retrieving but is rewritable more than 1000 times unlike the CD-R.
This CD-RW is a kind of phase-change optical disk, and an inorganic protective layer, a phase-change recording layer, an inorganic protective layer and a reflective layer are piled up in this order on a transparent resin substrate on which a guide groove is formed in advance, and further a protective layer made of a photo-curing resin is formed thereon.
The entire surface of the recording layer is once treated into a crystalline to establish an erased condition. For recording, a recording layer in a guide groove is irradiated with high-power laser light to change the crystalline of the recording layer so that an amorphous mark is formed to produce a reflectance variation with respect to a laser non-irradiated portion. The formed mark portion is irradiated with low-power laser light to detect a variation in reflectance, thereby retrieving the information recorded. That is, the recorded mark is substantially equivalent in function to a pit in the aforesaid CD available only for retrieving.
The CD available only for retrieving has an advantage in that it can supply a large volume of application software or the like at a low cost, but it rejects writing. On the other hand, as mentioned above, the CD-RW accepts the writing and functions as large-capacity record media, and has the format content normalized, coupled with being excellent in interchangeability with the CD available only for retrieving and very easy to handle, but is unsuitable for supply of a large volume of software at a low cost.
Meanwhile, in general, in a case in which a CD-RW writer is mounted in a personal computer, a CD-ROM or the like is not mounted simultaneously therein, but only the CD-RW writer is mounted therein; therefore, in most case, the CD available only for retrieving and the CD-RW cannot be put in operation at the same time. In this case, for recording the data produced/processed using application software distributed through the CD available only for retrieving, there is a need to once fetch the CD available only for retrieving from the drive for replacing it with a CD-RW.
Accordingly, a problem exists in that the recording of data on a CD-RW through application software distributed by a CD-ROM requires complicated procedures.
As means of solving this problem, there has been known an approach in which application software or the like is previously recorded one by one on a CD-RW through the use of a recording device and then distributed. However, this approach creates a problem in difficulty on mass production of a medium, and encounters a possibility of erasing of the once recorded application software in error, and for this reason, it does not reach a practical solution.
Japanese Examined Patent Publication No. 7-122935 discloses a technique on an optical recording medium having a ROM area and a RAM area on the same plane.
However, the technique disclosed in this publication involves forming an organic material recording film producing a recording layer only on the RAM area serving as a recordable area. In a case in which the film arrangement alters between the RAM area and the ROM area, although it is easy to separately control signal values read out from both the areas, there is a need to form a film in a state where a masking tool is set on each substrate to cover the ROM area, which has a detrimental effect on manufacturing. Moreover, when the position or size of the ROM area changes, there is a need to change the mask accordingly. Therefore, the technique is undesirable also in this respect.
In addition, the column xe2x80x9cProblems to be Solved by the Inventionxe2x80x9d in this Publication says xe2x80x9can application on an optical disk in which a recording layer made of an organic material is formed over an area comprising a ROM area available only for retrieving and a recordable RAM area and which is interchangeable with a compact disk was made as Japanese Patent Application No. 2-36190xe2x80x9d. However, since the recording layer is made of an organic material and a dye layer is formed even on the ROM area important for information, as mentioned in the column xe2x80x9cProblems to be Solved by the Inventionxe2x80x9d of the Publication, the ROM area tends to come under the influence of optical discoloration of the dye; therefore, this is undesirable.
Still additionally, Japanese Examined Patent Publication No. 7-70089 discloses a technique on an optical information carrying disk in which a recording layer, where information recording depends on variation of crystalline stemming from light irradiation, is provided on a surface of a substrate retaining information recorded in the form of embossed dots.
However, this technique involves a so-called phase-change recording layer, employed in place of a reflective layer in order to achieve partial correction, updating and addition of information, and is remote from formation of a ROM area and a RAM area on the same surface.
The present invention has been developed in consideration of the above-mentioned problems, and it is therefore an object of the invention to provide a rewritable compact disk having a ROM area and a RAM area and a manufacturing method thereof, capable of realizing both utilization of application software or the like and recording of data through the use of one CD-RW writer while maintaining interchangeability with a CD-RW.
In accordance with a first feature of the prevent invention, there is provided a rewritable compact disk having at least a phase-change recording layer on a substrate, characterized in that
a recordable, erasable and retrievable RAM area and a ROM area available only for retrieving are provided on the same disk surface,
the phase-change recording layer is formed in each of the RAM area and the ROM area and a wobble groove is made in the RAM area, and further a crystalline portion of the phase-change recording layer is made as a non-recorded state/erased state while an amorphous portion thereof is made as a recorded state, with the irradiation being carried with recording light out so that an amorphous mark is formed in the groove to record EFM information,
in the ROM area, EFM information is recorded in the form of a pre-pit string, and
when measured using a wavelength of 770 to 790 nm and an optical pickup whose objective lens numerical aperture is 0.49 to 0.51,
a ratio |I1xe2x88x92I2|/|I1xe2x88x92I2|a of values of push pull signals before and after recording of an EFM signal in the RAM area is 1.05 through 2.0, or a ratio |I1xe2x88x92I2|a/|I1xe2x88x92I2|ROM of a value of a push pull signal after recording in the RAM area to a value of a push pull signal in the ROM area is 0.78 through 1.3.
Particularly, it is preferable that a modulation amplitude of a 11T signal of the EFM signal in the ROM area is 0.55 through 0.95.
In addition, preferably, a ratio (m3/m11) ROM of a modulation amplitude of a 3T signal of the EFM signal to a modulation amplitude of a 11T signal thereof in the ROM area is equal to or more than 0.45.
Still additionally, preferably, a modulation amplitude of a 11T signal of the EFM signal in the RAM area is 0.60 through 0.90.
Preferably, a ratio (m3/m11) RAM of a modulation amplitude of a 3T signal of the EFM signal to a modulation amplitude of a 11T signal thereof in the RAM area is equal to or more than 0.45.
Moreover, preferably, a ratio RtopROM/RtopRAM of maximum reflectances of the ROM area and the RAM area is 0.7 through 1.45.
Still moreover, preferably, a radial contrast value in the ROM area is 0.30 through 0.60.
Preferably, a pre-pit string in the ROM area has an wobble. In addition, preferably, a normalized wobble signal NWSROM obtained from the wobble in the ROM area is 0.035 through 0.060.
Still additionally, preferably, the pre-pit string in the ROM area has a pit depth of 60 to 100 nm and a pit width of 0.45 to 0.70 xcexcm.
Moreover, preferably, the wobble groove in the RAM area has a groove depth of 30 to 50 nm and a groove width of 0.40 to 0.60 xcexcm.
In accordance with a second feature of the prevent invention, there is provided a rewritable compact disk having at least a phase-change recording layer on a substrate, characterized in that
a recordable, erasable and retrievable RAM area and a ROM area available only for retrieving are provided on the same disk surface,
the phase-change recording layer is formed in each of the RAM area and the ROM area and a groove (groove having a wobble) is made in the RAM area, and further a crystalline portion of the phase-change recording layer is made as a non-recorded state/erased state while an amorphous portion thereof is made as a recorded state, with the irradiation being carried out with recording light so that an amorphous mark is formed in the groove to record EFM information,
in the ROM area, EFM information is recorded in the form of a pre-pit string,
the pre-pit string in the ROM area has a pit depth of 60 to 100 nm and a pit width of 0.45 to 0.70 xcexcm, and the groove (wobble groove) in the RAM area has a groove depth of 30 to 50 nm and a groove width of 0.40 to 0.60 xcexcm.
In accordance with a third feature of the present invention, there is provided a preferred method of manufacturing this rewritable compact disk, comprising carrying out irradiation with laser light for exposure according to a pre-pit string and groove to be made in a photoresist film formed on a substrate and developing the photoresist film for producing a master having the formed pre-pit string and groove, producing a stamper on the basis of the master, forming a substrate having the pre-pit string and the groove on the basis of the stamper, and forming a phase-change recording layer thereon,
characterized in that, in irradiating the photoresist film with the laser light according to the groove, the irradiation for the exposure is carried out while oscillations are made 2.5xc3x97106 times/m or more but 25xc3x97106 times/m or less in directions perpendicular to a traveling direction of the laser light.
In accordance with a fourth feature of the present invention, there is provided another preferred method of manufacturing this rewritable compact disk,
comprising carrying out irradiation with laser light for exposure according to a pre-pit string and groove to be made in a photoresist film formed on a substrate and developing the photoresist film for producing a master having the formed pre-pit string and groove, producing a stamper on the basis of the master, forming a substrate having the pre-pit string and the groove on the basis of the stamper, and forming a phase-change recording layer thereon,
characterized in that, in irradiating the photoresist film with the laser light according to the groove, the irradiation is carried out with a plurality of laser beams for the exposure so that the adjacent laser beams partially overlap in a direction perpendicular to a traveling direction of the laser light.